1. Field of the Invention
The present invention relates to a method for manufacturing a cup-shaped container having gas barrier properties by injection molding in a state of disposing a label film having gas barrier properties around a trunk of the container.
2. Description of the Related Art
As containers made of a synthetic resin material, there are multilayer containers made of two different kinds of resins to provide an objective function, and containers provided with a film having an objective function on the outer surface of the container. The multilayer containers include two container surface layers (an inner surface layer and an outer surface layer of the container) made of one of the resins, and a container intermediate layer that is disposed and sandwiched between the two container surface layers and made of the other resin that can exert the objective function.
In the containers provided with a film on the outer surface of the container, the film having the objective function is disposed on the outer surface of the container by in-mold molding.
For example, Patent Literature 1 describes a multilayer container made of a surface layer forming resin, an oxygen barrier resin, and an adhesive resin that are injected from one injection molding nozzle, so as to form a layer of the oxygen barrier resin as an intermediate layer.
Patent Literature 2 describes a multilayer container in which an oxygen barrier resin layer is formed between two resin layers of a container surface resin by stacking the resins fed by a plurality of injection molding machines into layers using a laminar flow member (torpedo) and feeding the resins into a mold.
Patent Literature 3 describes a multilayer container manufactured by feeding resins from an injection molding nozzle so as to make a polyolefin resin layer, a gas barrier resin layer, and another polyolefin resin layer and arrange them from the outer surface to the inner surface the container.
Moreover, Patent Literatures 4 and 5 describe a multilayer container formed by in-mold molding. Patent Literatures 4 and 5 show that, while injecting resins, a film or metal foil is disposed in a mold at a container trunk forming portion at a portion to be the outer or inner periphery of a container trunk portion, and also that when a container bottom forming portion is molded, a synthetic resin having gas barrier properties or light blocking properties is co-injected together with a synthetic resin for the container main body.
[Patent Literature 1] Japanese Patent Application Laid-Open No. Hei. 04-031018
[Patent Literature 2] Japanese Utility Model Application Laid-Open No. Hei. 05-026340
[Patent Literature 3] Japanese Patent Application Laid-Open No. 2008-307846
[Patent Literature 4] Japanese Patent Application Laid-Open No. 2006-056559
[Patent Literature 5] Japanese Patent No. 5050679
By the way, in the container industry, containers having thin walls have been developed from the viewpoint of a reduction in weight and cost of the containers.
As to the multilayer containers having the intermediate layer described in the patent literature 1-3, however, it is technically difficult to form the intermediate layer uniformly in the entire container, while thinning its walls. Also, under the present circumstances, multilayer molding that is conditional on thin walls is hard to use as a mass production technique for the containers, which requires stability for mass production.
Although a multilayer preform is known as a similar molded article by multilayer molding (see Japanese Patent No. 4953178), the preform itself is a molded article having a thick wall, which is to be stretched and thinned to a final thickness of a container by stretch blowing or the like. The multilayer preform without modification cannot be applied as is to a thin wall multilayer molding technique to injection mold multilayer containers.
On the other hand, in recent years, as described in Patent Literatures 4 and 5, a film having gas barrier properties is integrated with a molding resin of a container main body as the exterior of a container, to improve gas barrier properties or light blocking properties. The technique of molding a gas barrier layer from a resin having gas barrier properties is applied to only the bottom portion of a container at which the film is difficult to be integrated.
However, to wrap the film around the periphery of the container trunk portion in an integral manner, bonded faces are necessarily required in the film at its ends. Depending on the thickness and manner of overlapping of the bonded faces, it is difficult to impart expected gas barrier properties at a bonded portion.